US2364913A - Solid fuel burner - Google Patents

Description

Dec. 12, 194'4. E. c.' PETERSON 'ITAL 2,364,913

SOLID FUEL BURNER Fl'ed Dec. 6, 1940 Patented Dec. 12, 19'44 SOLID FUEL BURNER Earl C. Peterson and Lester V. Baumgart, Minncapolis, Minn., assignors to Home Heaters, Inc., Racine, Wis., a corporation of Wisconsin Application December 6, 1940, Serial No. 368,798

1 Claim.

This invention pertains to the art of burning solid fuel, and is particularly adapted for the purpose of burning cheap, high volatile coals efficiently and without [producing objectionable smoke.

Because the 4coal burners now available require coals meeting specified characteristics, a great deal of easily available, low-cost coal is not being utilized for domestic heating.` It is an object of this invention to provide a heating unit which makes it possible to utilize low-cost, high-volatile coal efficiently and burn such coal in a smokeless manner. It is a further object of this invention to devise a solid fuel burning unit which is applicable to, and may be used as an adjunct of, the conventional domestic heating furnace. It is a further object of this invention to devise a solid fuel burner which admits burning gases of combustion into the conventional domestic furnace thru the usual firing door opening thereof. 'It is a further object to devise a burner comprising primary and secondary combustion chambers and a coal hopper, the coal hopper or magazine `being lined with a refractory having a high specic heat while the secondary combustion chamber has a low specific heat lining material. A further object is to devise a burner in which the gases of combustion are given an eddy current flow tending to mix such gases thoroughly with secondary air. Further objects are to devise a Iburner comprising a fuel hopper, primary and secondary combustion chambers, means for feeding primary and secondary air thereto, means for repeatedly changing the direction of ow of the burning gases in order to mix them thoroughly with air, and means to complete the combustion within a conventional furnace with a high degree of efficiency and cleanliness. A still further object of this invention is to provide a new and improved refractory lining material for burners and furnaces. Other objects will become apparent from the following description.

In the drawing illustrating a specific embodiment of `this invention, Fig. 1 is a vertical, central section of the solid fuel burner of this invention, taken on line I-I of Fig. 2; Fig. 2 is a horizontal section taken on line II-II of Fig 1; Fig. 3 is a section on line III-III of Fig. 1; and Fig. 4 is a section on line IV--IV of Fig. 1.

Ihe body of the solid fuel Iburner comprises front and back walls I0, Il and side walls I2, I3. The forward part of the unit forms a fuel hopper I5, the walls of which flare outward in a downward direction, as shown. 'Ihis is `for the purpose of permitting the fuel contained therein to fall downward freely under the action of gravity, minimizing friction between the fuel and the walls of .the hopper. The fuel hopper is closed Iby a sealed cover I5, and is lined with high specie heat refractories Il, which are described below. Beneath the hopper I5 and extending beyond it are located a plurality of triangular shaking grates I8, which are arranged to be agitated in a known manner. Grrates` I8 are hollow, and are provided with openings I9 at both ends, and additional apertures 20 at the inner ends thereof. Referring to Fig. 3, it will be noted that side wall linings 22 of hopper I5 are supported by means of linings 23 which are laterally offset outward from linings 22, providing shoulders 2d between the hopper and primary combustion chamber.

Intermediate wall 2l divides the hopper I5 from secondary combustion chamber 28. When the .primary combustion chamber and hopper are filled with coal, an air passage is. left adjacent shoulder 24, due to the angle of repose of the coal. This passage permits air to pass from the front o-f the unit, after entering thru the opening of damper 30, passing around the fuel in .the hopper and primary combustion chamber, to aid combustion in secondary combustion chamber 28. All of the liners may be supported by means of angle irons 32 carried by the base of the burner.

Intermediate wall 2l extends downward, leaving a space between the bottom of this wall and grate I8 such that, at its normal angle of repose, the fuel placed in the hopper will leave a part of the grate surface free for access of air into secondary combustion chamber 28. At its upper end, secondary combustion chamber 28 connects with an elbow conduit 33, which connects with another elbow conduit 34. Both elbow conduits 33, 34, as well as the linings of the secondary combustion chamber 28 are made of a low heat capacity refractory material. Conduits 33, 34 connect the upper end of secondary combustion chamber 28 with the interior of a conventional furnace 3l, passing thru the regular firing door opening 38 thereof, and directing the burning gases downward withinthe furnace thru opening 35. The furnace may be lined with iireclay 4|] to provide a round pot to turn the gases upward. The burner may be encased in sheet metal To start a fire in the burner, kindling and wood are placed on grates I8 beneath hopper I5, and ignited. After the wood is burning freely.

coal may be deposited on the wood fire, and gradually built up until the hopper is substantially full of coal. The fire will burn readily in primary combustion chamber 26, distilling combustible gases from the coal in primary combustion chamber 26. These gases flow as indicated by the arrows thru secondary combustion chamber 28, where they mix with Yair admitted thru hollow grates I8 and adjacent shoulders 24. The air passes into secondary combustion chamber 28 thru the olpen ends of grates I8 and also thru the smaller openings 20, which serve to distribute the air uniformly thruout the secondary combustion chamber. The air, mixed with burning gases of combustion, is caused to mix therewith more uniformly due to change in direction of ow as the gases turn upward in secondary combustion chamber 28, again at the turn of conduit 33, again at the downward bend of conduit 34, and again upon contacting the rounded interior of furnace lining 40 and turning toward the flue. These changes in direction of gas flow serve to mix the combustion gases more intimately with air. In addition, the construction shown make it possible to insert the outlet of the. solid fuel burner of this invention into the firing door of the conventional furnace found in almost every house.- hold. It will be noted that a number of refractory rings or shims 46 are provided between the secondary combustion chamber and the conduit 33, in order that the height of conduit 33, 34 may be varied to meet the requirements of any given furnace. The adjustment of the height of conduit 33, 34 by means of the rings 45 is made prior to enclosure thereof and the various refractory walls in the heat insulating material 42 and the sheet metal 43.

When in operation, the fuel in primary combustion chamber 26 is usually. in an incandescent state, and combustion takes place thruout secondary combustion chamber 28, inside conduits 33, 34 and within the furnace 31. If the secondary combustion chamber and conduits were made of or lined with material having a high specific heat, it would take an appreciable time to heat the walls thereof to a temperature which would support efficient combustion. In the meantime soot would collect on these: walls, and the combustion would be incomplete, resulting in smoke and more soot. We have discovered that-the resulting combustion is much more efficient if the Walls of the secondary combustion chamber and conduits 33, 34 are made of, or lined with, a refractory having a low specific heat. On the other hand, the walls of hopper l should be made of, or lined with, a material having a high specific heat, since this would tend to keep these walls cooler and discourage combustion Within the hopper.

The selection of refractories is of extreme irnportance, especially' where the problem is to burn cheap fuels without objectionable smoke. By 1ining the hopper with a material having a high specific heat, the heat transfer thru the hopper is retarded, thereby resulting in improved eiliciency. On the other hand, by lining the secondary combustion chamber with material having a low specific heat, the lining of this chamber will reach a high temperature in a very short time, thus preventing deposition of soot such as would occur if the hot gases of combustion were to impinge upon a relatively cool surface.

While Various materials may be used as refractories, one satisfactory composition consists of 90 parts of crushed rebrick or refractory clay sinter, 10 parts of silicon carbide, one part of aluminum sulphate, l5 parts of aluminite cement, and 15 parts of reclay, for lthe lining for the hopper. For the secondary combustion chamber and conduits to the furnace, the preferred composition would comprise the same ingredients but containing '75 parts of crushed rebrick or refractory clay sinter and 25 parts of silicon carbide. This will provide the necessary heat capacity characteristics specified above. It has also been found that if these ingredients are mixed with enough water to bind or become lpartly sticky, and are then vibrated 'briefly at high speed to make precast plates or slabs, the silicon carbide component appears to be brought to the surface of the plates or slabs. This is highly to be desired, since the presence of silicon carbide in the surfaces` adjacent to the burning gases appears to have a catalytic effect in causing more perfect smokeless combustion. Ccncentrating the silicon carbide component of the composition at the surface of the plates or slabs therefore results in the same effect as using a larger proportion of silicon carbide, without the attendant disadvan tages o-f increased cost and increased brittleness. The composition of the refractories per se is not claimed herein.

It has been found that because of the intimate mixture of air and gases of combustion obtained with this construction, and the intermixture of air and gases due to repeated changes in the direction of gas flow, and because of the materials used, a uniform, efficient, smoke-free combustion is attained in a unit which may be attached to a conventional furnace for easily and efficiently burning high volatile coal which has hitherto been generally considered unacceptable for domestic heating. The hopper makes it possible to operate this burner for relatively long periods Without attendance.

While repeated reference has been made to domestic heating, it is to be understood that the invention is also adaptable to commercial and industrial utilization. used herein is applicable to hot water and steam boilers, as well as-warm air furnaces. .While a specific construction has been described for purposes of illustration,' the invention is to be construed as broadly a-s the claims appended hereto ipermit.

It is claimed and desired to protect by Letters Patent:

A solid fuel .burner comprising a substantially rectangular casing provided with substantially vertical outer Walls, a substantially vertical intermediate Wall dening a hopper and a primary combustion chamber on one side thereof and a vertically directed secondary combustion chamber on the other side of said intermediate wall, means for conducting air to both said combustion chambers, a horizontally directed conduit communicating with the upper end of said secondary combustion chamber for directing the gases of combustion therefrom, and a plurality of supporting members interposed between the upper end of said secondary combustion chamber The word furnace as

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